Tackling a Top‑Cover Leak on a CAV DPA Injection Pump

[MikePhua]

When diesel oozes from the top of a CAV DPA (Distributor-type Pump Assembly), it typically indicates a compromised seal or mechanical wear. Though the fix may seem daunting, a structured approach can restore reliability—and extend the life of your engine’s fuel system.
Understanding Why the Top Cover Leaks
Several clues point to the underlying issue:

• Worn or deteriorated O‑ring or gasket that seals between the top cover and pump housing.
  
• Deformation or warping of the metal mating surfaces, causing an uneven seal.
  
• Loose or overtightened fasteners, leading to uneven compression of the seal.
  
• Cracked cover or housing, from vibration, age, or stress.
  

Leaks may only appear under pressure or when the pump is operating, masking their presence when idle.
Step‑By‑Step Repair Process
Approach the fix methodically:

• Ensure safety first:
  • Let the engine cool completely and relieve any fuel system pressure.
    
  • Work in a well-ventilated area, free from ignition sources.
    
• Remove the top cover:
  • Loosen bolts in a crisscross sequence to avoid distorting the cover.
    
  • Gently lift—binding indicates internal pressure or warped components.
    
• Inspect the gasket or O‑ring:
  • Look for cracks, hardening, or compression set.
    
  • Seal materials lose flexibility over time, inviting leaks.
    
• Assess metal surfaces:
  • Check both the underside of the cover and the pump housing for pitting, gouges, or uneven mating surfaces.
    
  • A clean, flat surface ensures a proper seal.
    
• Replace sealing components:
  • Choose high-quality, fuel-rated O‑rings or gaskets matching OEM specs.
    
  • Lightly coat the seal with compatible diesel-grade lubricant to aid seating.
    
• Reinstall with precision:
  • Torque bolts as specified—cross pattern to maintain even pressure.
    
  • Avoid overtightening, which can split gaskets or crack the housing.
    
• Test for leakage:
  • Run the engine briefly under idle and moderate throttle, watching for fuel seepage.
    
  • Repeat checks after returning to operating temperature.
    

A Practical Repair Anecdote
One fleet technician noticed his delivery truck dripping diesel right from the pump’s top seam. After replacing the brittle, discolored gasket and carefully lapping the cover to remove minute surface pitting, he resealed and torqued the assembly properly. The leak vanished, and the truck ran cleanly through the next long haul—even under repeated cold starts and high-load conditions.
Glossary of Technical Terms

• CAV DPA pump – A type of distributor-style diesel injection pump common in older engines, featuring a top-mounted rotor and distributor head.
  
• O‑ring – A circular rubber seal that fits between mating parts to prevent fluid escape.
  
• Gasket – A flat sealing material, often fiber or metal-reinforced, used when broader surface sealing is needed.
  
• Cover warping – Slight deformation of the pump’s top lid, usually from age or uneven bolt tension, leading to imperfect sealing.
  
• Mating surface – The area where two components touch and form a seal; flatness here is essential for leak prevention.
  

A seemingly minor fuel leak at the pump’s top cover can escalate into serious safety and performance concerns if left unchecked. With careful inspection, gasket replacement, and attention to fitting integrity, the repair is straightforward—and restoring leak-free operation ensures engine reliability and cleaner service. Let me know if you'd like tips on refilling once the pump is reinstalled or on torque specs for specific pump models!